Run and compare benchmarks after successful ci-build

.travis.yml

@@ -7,3 +7,5 @@ env:
 go: [1.12.x, 1.13.x]
 services:
   - redis-server
+after_success:
+  - bash ./.travis/benchcmp.sh

.travis/benchcmp.sh

@@ -0,0 +1,15 @@
+if [ "${TRAVIS_PULL_REQUEST_BRANCH:-$TRAVIS_BRANCH}" != "master" ]; then
+    REMOTE_URL="$(git config --get remote.origin.url)";
+    cd ${TRAVIS_BUILD_DIR}/.. && \
+    git clone ${REMOTE_URL} "${TRAVIS_REPO_SLUG}-bench" && \
+    cd "${TRAVIS_REPO_SLUG}-bench" && \
+    # Benchmark master
+    git checkout master && \
+    go test -run=XXX -bench=. ./... > master.txt && \
+    # Benchmark feature branch
+    git checkout ${TRAVIS_COMMIT} && \
+    go test -run=XXX -bench=. ./... > feature.txt && \
+    go get -u golang.org/x/tools/cmd/benchcmp && \
+    # compare two benchmarks
+    benchcmp master.txt feature.txt;
+fi